Transcriptional dynamics and cellular function of p53 pulses Healthy cells avoid becoming tumors by protecting their DNA from harmful alterations. When DNA damage occurs, the tumor suppressor protein p53 orchestrates a complex network of signaling pathways that either halts progression through the cell cycle and attempts to repair the damaged DNA, or triggers cellular death. It has been observed that certain dangerous forms of DNA damage, such as double strand breaks caused by ionizing radiation, cause p53 to undergo a series of wave-like pulses. The molecular mechanisms that generate these pulses are now reasonably understood, but their functional importance is not known. This proposal investigates the hypothesis that p53 pulses are important for the regulation, selection and timing of the transcription of p53's target genes and that these changes in expression promote differences in cellular outcome. This hypothesis will be tested by directly perturbing p53 pulse dynamics and collecting time-series measurements of gene expression. A customized set of computational strategies will be used to identify groups of genes that are differentially regulated by pulse dynamics;functional pathways activated by pulse- driven changes in gene expression;and differences in transcription factor coregulation of p53 target genes during successive pulses. Specific predictions of differentially activated genes, functional pathways, and p53 cofactors will be confirmed experimentally in both cell populations and individual cells. These experiments will focus specifically on distinguishing cells that are undergoing cell cycle arrest, cell death, senescence, or DNA repair in response to p53 pulses. Since the "decision" to enter one of these cellular states is largely determined by the transcriptional activity of p53, understanding the transcriptional response to p53 pulses will further our understanding of how this highly versatile transcription factor selects between alternate cell fate decisions. This knowledge will guide the design of therapeutic methods that alter p53 dynamics in order to rescue its proper function in stemming tumor development. PUBLIC HEALTH RELEVANCE: The p53 tumor suppressor protein has an unquestionably important role in guarding against cancer, reflected by the fact that more than half of human cancers contain mutations in p53. This proposal aims to understand how p53 dynamics alter gene expression and ultimately control cell fate. Understanding this relationship will guide the design of therapeutic methods that alter p53 dynamics in order to rescue its proper function in stemming tumor development.